The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams, such as slab urethane foams, are usually made by the reaction of a polyhydric alcohol with an alkylene oxide, typically ethylene oxide and/or propylene oxide, to a molecular weight of about 2,000 to 5,000 and above. These polyols are then reacted with polyisocyanate in the presence of water or other blowing agent such as fluorocarbons to obtain polyurethane foams. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane, for example, by using a polymer polyol as the polyol component. Conventional polyols may be used as the dispersing media or base polyol in these polymer polyols.
For example, polymer polyols containing polymers of vinyl compounds such as styrene, acrylonitrile or a mixture of the two (abbreviated as SAN monomers), or of polyurea polymers, such as those prepared from toluene diisocyanate (TDI) and hydrazine in conventional polyols have been included to improve the properties of the polyols, and thus, the properties of the resulting foam. Polyurethane foams with higher load bearing properties (ILD--indentation load deflection, and CFD--compression force deflection) may be produced in this manner. It would be desirable if polymer polyols could be prepared which would be stable and have low viscosities. Stability is important to the storage life of the polyols so that they will remain homogeneous before they are used to make the polyurethane foams. Low viscosities and small particle sizes are important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
It would further be desirable if styrene/acrylonitrile polymer polyols could be synthesized which would have large SAN ratios. The substitution of styrene for acrylonitrile in these polymer polyols helps prevent discoloration during the cure of the polyurethane, and also helps improve flame retardability of the resultant foams. However, the stability of the polymer polyols decreases with increasing styrene to acrylonitrile ratios. That is, the components tend to separate upon standing during storage. Viscosity and particle size are also typically adversely affected with high styrene contents.
To prepare dispersions with high styrene contents and high solids contents, it is the practice in the art to employ polyols which contain specified and ostensibly critical amounts of induced unsaturation as shown in U.S. Pat. Nos. 3,823,201; 4,454,255; 4,690,956; and others. Many of these teachings also require the use of a chain transfer agent, such as an alkyl mercaptan. In U.S. Pat. No. 4,855,330 it was discovered that epoxy modified polyols were useful as base polyols for preparing polymer polyols with high styrene contents. Patents relating to these type of modified polyols and polymer polyols include U.S. Pat. Nos. 4,316,991; 4,539,378; 4,539,339; 4,495,341; 4,647,624; and 4,585,831, and Japanese Patent Publication No. 24,255/71.
In U.S. Pat. No. 4,891,395 it was found that epoxy modified polyols were useful as dispersants for preparing polymer polyols with high styrene contents in an unmodified base polyol. The epoxy modified polyols described above were prepared from the reaction of a polyol with an epoxy resin. The ratio of hydroxy groups of the polyol to the epoxy groups of the resin was relatively high, so that excessive crosslinking did not occur and viscosity of the product was low.